Method for rolling strip metal



July 18, 1967 c, w, K|NG 3,331,232

METHOD FOR ROLLING STRIP METAL Filed Dec. 16, 1964 3 Sheets-Sheet 1 Q N LL "1 INVENTOR. CLAUDE n. KING his 2 July 18, 1967 c w, KNG 3,331,232

METHOD FOR ROLLENG STRIP METAL Filed Dec. 16, 1964 5 Sheets-Sheet 2 INVENTOR.

CLAUDE m KING BYSe 41's 2::

July 18, 1967 c. w. KING METHOD FOR ROLLING STRIP METAL 5 Sheets-Sheet 3 Filed Dec. 16, 1964 IS'LJ I5 FIG. 4

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United States Patent 3,331,232 METHOD FOR ROLLING STRIP METAL Claude W. King, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware Filed Dec. 16, 1964, Ser. No. 418,787 7 Claims. (Cl. 72-365) ABSTRACT OF THE DISCLOSURE roll stand and is reduced to the desired gauge thickness and surface finished, When the rolls in the second roll stand are replaced, this second roll stand becomes the finishing roll stand and the first roll stand becomes the roughing roll stand.

This invention relates to metal working and, more particularly, to a tandem reversing hot strip rolling mill.

Steel plants that can economically produce a small annual tonnage of flat rolled products are needed in many parts of the world, especially in the newly emerging and underdeveloped countries. Use of conventional types of continuous strip mills in these areas is uneconomical and impractical because of the very limited market and ertremely high cost of the products. Reversing hot strip mills could present a solution to the problem except that the conventional reversing hot strip mill cannot produce a satisfactory, tight, smooth, oxide surface. The surface quality of the product of such mills is generally unacceptable for many purposes, and this is particularly true where extremely light gage products, such as 38 gage strip material, are to be produced for galvanizing purposes. The hot rolled strip that is produced in the conventional reversing hot strip mill, cannot be cold reduced to the required light gage unless quality is sacrificed because the product is full of pin holes.

The present invention, however, overcomes these problems and presents an economical, medium capacity, reversing hot strip mill that produces not only a product having the fully acceptable surface quality which is required for the light gage strip material, but also a product that is as thin gage as is commercially usable.

The invention contemplates a reversing hot strip mill that imparts to the product the same quality of smooth, tight, oxide surface tha is produced by either the fully continuous, or semi-continuous hot strip mill. Two conventional roll stands are placed tandemly adjacently to each other and are driven by a single drive motor through a set of drive gears. The first roll stand is used initially as an intermediate roughing stand and the second roll stand is used as the finishing stand. After a period of use, when the roughing rolls are worn and require replacement, the newly installed rolls in the first stand become the finishing rolls, and the older finishing rolls become the intermediate roughing rolls. Associated with each roll stand are a single drive motor, shafting, gears and pinions to simultaneously drive both of the rolls. Also associated with the roll stands are the usual driven table rolls, pinch rolls, coil furnaces, and descaler sprays.

For a further understanding of the present invention and for advantages and features thereof, reference may be made to the following description taken in conjunction with the accompanying drawings forming a part of this application.

3,331,232 Patented July 18, 1967 FIG. 1 is a schematic elevational view of a hot strip mill in accordance with a preferred embodiment of the present invention;

FIG. 2 is a schematic plan view of the mill of FIG. 1;

FIG. 3 is a schematic diagram showing the rolling sequence in one application; and

FIG. 4 is a schematic diagram showing the rolling sequence in another application.

A reversing hot strip mill, designated generally as 11 in FIG. 1 includes a pair of roll stands 13, 15, designated hereinafter as No. 1 and No. 2 roll stands respectively; two sets of power driven table rolls 17, 19; two sets of power driven pinch rolls 21, 23; and two sets of coiling furnaces 25, 27. The table rolls 17 and the coiling furnace 25 are designated hereinafter respectively as No. 1 table rolls and No. 1 coiling furnace. The other table rolls 19 and coiling furnace 27 are designed hereinafter as No. 2 table roll and No. 2 furnace.

Each of the four-high roll stands 13 and 15, which may be conventional, comprises a frame structure 16, adapted to support a pair of opposed upper middle rolls 29 and lower middle roll 31, each of which engages a larger upper outer roll 33 and a lower outer roll 35; all of the rolls being vertically aligned as shown. The lower middle 31 and outer 35 rolls are journally fixed in the frame, but the upper middle 29 and outer 33 rolls are journally movably supported in the frame 16, and are vertically movable in response to the action of a conventional screwclown motor driven mechanism 37.

The roll stands 13 and i5 are supported on a subjacent central shoe plate 39, and subjacent outer shoe plates 41, 43, about as shown in FIG. 1. These shoe plates 39, 41, 43 are fixed to a suitable supporting foundation 45 in a conventional manner.

The roll stands 13 and 15 are spaced apart a convenient distance which, in a typical installation, may be about 24 inches. The roll stands 13, 15 are 50 disposed that a tangent plane to the top of the lower middle rolls is substantially horizontal. The roll stands 13, 15 are provided also with a conventional water spray nozzle system 47, for the purpose of cooling the roll surfaces 29, 31, 33, 35.

As mentioned previously, each roll stand is operatively associated with its respective table rolls, pinch rolls, and coiling furnace. Now then, because the table rolls 17, pinch rolls 21, and coiling furnace 25 are substantially the same as the table rolls 19, pinch rolls 23, and coiling furnace 27, a detailed description of each is not necessary. it suffices, then, to describe only the table rolls 17, pinch rolls 21, and coiling furnace 25, designated hereinbefore as No. 1 table rolls, No. 1 pinch rolls, and No. 1 coiling furnace.

For convenient reference hereinafter, the left end of the mill 11, as viewed in FIG. 1, will be considered as the front end, and the right side as the rear end of the mill.

The No. 1 table rolls 17 includes the usual frame structure 49 that is conveniently supported by subjacent members 51 to the support foundation 45. The frame structure 49 journaliy supports a plurality of power driven rollers 53, which are disposed to be undertangent to the aforementioned lower middle rollers tangent plane. The table rollers 53 are driven by the usual electric motor system (not shown) connected to drive shafting 54, for the purpose of conveying a strip of steel from one coil furnace, through the roll stand, to the other coil furnace, in the manner described more fully hereinafter.

The No. 1 table rolls 17 is disposed conveniently adjacent the No. 1 roll stand 13 so that the strip of metal will be horizontally supported as it emerges from and approaches the respective roll stand.

The coiling furnace 25 is also conventional and includes a refractory lined housing 55 in which is suitably journalled a conventional coiler mechanism 57 on which the hot strip material is wound. The furnace 25 is heated in the conventional manner (not shown) to a predetermined selected temperature and the material which is coiled therein is maintained at that selected temperature. The furnace 25 is supported on suitable adjacent foundation structure 59, and is disposed generally above the table rolls 17, as shown in FIG. 1. A conventional type of strip guide shoe 61 is typically mounted to the table roll frame structure 49, and is operable, in the manner described hereinafter, by a system of cranks and links 63 mounted on a drive shaft 65, for the purpose of guiding the hot strip into the coiling furnace and into engagement with the coiler mechanism 57.

Associated with each table rolls 17, 19 is a set of conventional pinch rolls 21, 23, respectively, which are conveniently located close to the coiling furnaces 25, 27, as shown in FIG. 1. Each set of pinch rolls comprises a fixed power driven lower roller 63, and a vertically movable power driven upper roller 65; the upper roller being movable vertically by means of a fluid actuated cylinder-piston arrangement 67, and a linkage system 69.

The intermediary roughing roll stand 13, and the finishing roll stand 15, are each driven (see FIG. 2) by No. l and No. I conventional pinion sets 71, 73, respectively. Both of the pinion sets 71, 73 are driven by a single electric motor 75, of suitable size and horsepower, which is drivingly connected by suitably journalled shafting 77 to both No. l and No. 2 sets of drive gears 79, 81. An

intermediary suitably journalled idler gear 83 is disposed between the drive gears 79, 8].. The gears 79, 81, 83, are, preferably, herringbone-type gears although, of course, other types of gears may be used if preferred. The conventional pinion sets 71, 73 are driven by suitably journalled shafting 85, 87, respectively and each pinion set drive both the upper and lower middle rollers 35, 37 of a respective roll stand 13, 15. Now, referring to FIG. 3, a slab or ingot 89, to be operated on in accordance with this invention, is forwarded in the usual manner to the hot strip mill 11. Before the slab is sent to the mill it has been previously roughed down the required width. Conventionally, it has a thickness of about 0.625 inch and would have been descaled, for example, by conventional high pressure high velocity descaling spray nozzles, before it reaches the reversing mill 11.

Before the ingot arrives at the reversing mill 11, the rolls of the No. 2 roll stand 15 are purposely spaced apart a distance of about one and one-half inches, to permit easy travel of the ingot therethrough. At the same time, the screw-down mechanism 37 on the No. 1 roll stand 13 would be set to make the first reduction from 0.625 to 0.375 inch.

In a typical operation, referring to FIGS. 1 and 3, the ingot would then enter the mill 11 from the front or left end and move to the right, toward the rear of the mill. On the first pass, the ingot would enter the No. 1 roll stand at a temperature of about 1850" F., be reduced in thickness, emerge therefrom, and freely pass through the open No. 2 roll stand 15. The ingot would thus receive a first reduction of about 40 percent on the first pass. The ingot would then be carried by the No. 2 power driven table rolls and the No. 2 pinch rolls toward the No. 2 coiling furnace 27. As the ingot approached the No. 2 coiling furnace, it would engage the previously actuated upwardly incilned guide shoe 61 and be guided into the coiling furnace wherein it would be wound upon the coiler 57 in the usual manner. As is well known, the purpose of the coiling furnace is to maintain the temperature of the slab or breakdown at a previously selected temperature which, in a typical application, may be in the range of about l700l800 F.

During the time the strip is coiled in the furnace and, as the trailing end of the strip leaves the No. 1 roll stand, the screw-down on No. 1 roll stand would be reset to make the second reduction. At the same time the driving motors of the No. 1 roll stand and the several table rolls would be reversed, and the ingot would then be withdrawn from the No. 2 coil furnace and directed by the pinch rolls and power driven table rolls toward the No. 1 roll stand. The ingot would again freely pass through the No. 2 roll stand and enter the No. 1 roll stand where it would be reduced in thickness to approximately 0.225 inch, also a 40 percent reduction. Upon emerging from the No. 1 roll stand the strip would be directed by the power table rolls and pinch rolls into the No. 1 coiling furnace 25. The temperature of the No. l coiling furnace likewise maintains the breakdown at a temperature of about 1700- i800 F.

During the time the coiled breakdown is in the No. 1 coiling furnace and, as the trailing end of the strip leaves the No. 1 roll stand, the screw-down on the No. 1 roll stand is reset at 0.148 inch for a third reduction. After reversing the motors as previously described, the No. 1 pinch rolls unwind the coiled breakdown and, together with the powered No. 1 table rolls, drive the breakdown toward the No. 1 roll stand. The breakdown is reduced about 34 percent on this pass by the No. 1 roll stand, again freely passes through the open No. 2 stand, and is received in the No. 2 coiling furnace. During the No. 3 pass, however, the strip would be descaled by the usual high pressure high velocity water jets of a conventional descaler 89, located adjacent the No. 2 pinch rolls 23 (sec FIGS. 1 and 2). Also, during the No. 3 pass, the screw-down on the No. 2 roll stand would be run down to a point where the upper 29 and lower 31 middle rolls are spaced apart a distance of about 0.375 inch, or slightly more than the thickness of the strip.

As the trailing edge of the strip leaves the No. 1 roll stand 13, and clears the No. 2 roll stand 15, during pass No. 3, the screw-down on the No. 2 roll stand 15 would be run down to a reduction setting of 0.105 inch, preparatory to the No. 4 pass. At the same time, the screwdown on the No. 1 roll stand 13 would be started upward and permitted to run until the middle rolls 35, 37 are spaced apart a distance of about one and one-half inches. This spacing will permit free travel thereafter of the breakdown, or strip, through the No. 1 roll stand.

To adjust the screw-down on the No. 2 roll stand should, in a typical installation, requires not more than three or four seconds. Those skilled in the art will recognize that it is entirely feasible to make this screw-down adjustment, within the reversing time which is the time required: to decelerate the strip as it coils in the furnace; to stop the strip completely; to reverse the several motor drives; and to again accelerate the strip to the desired velocity. In a typical installation, the time for reversing the movement of the hot strip will be about 6-8 seconds.

The hot strip is now uncoiled from the No. 2 coiling furnace and freely conveyed toward the No. 2 roll stand. On pass No. 4, the thickness of the strip is reduced from 0.148 inch to 0.105 inch, which is a 29 percent reduction. The strip is then conveyed, as before through the No. 1 roll stand and into the No. 1 coiling furnace. While in the No. l coiling furnace and as the trailing end of the strip leaves the No. 2 roll stand, the screw-down on the N0. 2 roll stand is reset at 0.090 inch, from the last and final pass No. 5. The strip is again conveyed from the No. 1 coiling furnace to the No. 2 roll stand, and therein is reduced 14.5 percent, to a thickness of 0.090 inch.

At the conclusion of the No. 5 pass, the strip 89a which now may be at a temperature of 1600 F., is passed down the usual run out table to a final coiler, thus bypassing the No. 2 coiling furnace.

As the trailing edge of the strip 89a leaves both the No. 1 and No. 2 roll stands, the No. 1 screw-down would be reset again to the initial reduction of 0.375 inch, and the screw-down on the No. 2 roll stands would be opened again to about one and one-half inches. Thus, the mill 11 is ready to repeat the step reduction cycle.

The versatility of the mill of the present invention is demonstrated by its capability of rolling slabs directly into strips without the first roughing stand, mentioned hereinbefore. In this instance, a slab 91 having a thickness for example of about 3.5 inches would be edged and descaled in the usual manner, and thereafter, passed through the intermediate roughing roll stand No. l, in the reversing manner described previously for 7 passes instead of 3. Reducing passes No. 1 and No. 2 however would be made on the No. 1 roll stand in the fiat state; that is to say, the slab would not be coiled during these two passes. After making the No. 2 pass the slab would again be edged and descaled by conventional apparatus (not shown) prior to making reducing passes No. 3 and No. 4. These passes also would be made without coiling. Following No. 4 pass the strip breakdown would be end cropped and again descaled by conventional apparatus prior to making pass No. 5. Passes Nos. 5, 6 and 7 would be made on the No. 1 roll stand along with coiling in the coiling furnaces, in the manner described previously. Passes No. 8 and No. 9 would be made on the No. 2 finishing stand in the manner described previously with coiling between these passes but not after pass No. 9.

The following draft schedule shows the percentage (approximately) reduction during each pass to reduce the 3.5 slab to a finished product.

Enter a 3.5" slab initially; the thickness is reduced on Pass No. 1 to 2.250", a 36% reduction;

Pass No. 2 to 1.400", a 37.5% reduction;

Pass No. 3 to 0.850", a 36% reduction;

Pass No. 4 to 0.625", a 36% reduction.

(Additional cropping and descaling may be needed after No. 4 Pass) on Pass No. 5 to 0.375", a 40% reduction; Pass No. 6 to 0.225", a 40% reduction; and Pass No. 7 to 0.148", a 34% reduction.

Passes No. 1-7 are made on the No. 1 roll stand. As Pass No. 7 is being made, the screw-down on No. l and No. 2 roll stand are set as described hereinbefore. Then, in stand No. 2, the strip 91a makes the final two finishing passes. The thickness is reduced on Pass No. 8 to 0.105, a 29% reduction; and Pass No. 9 to 0.090", a 14.5% reduction.

Thereafter, the strip 91a as a final product is run out to the final coiler.

In the usual single stand type reversing hot strip mill, the rolls are reducing material that ranges in temperatures from about 1850 F. it enters the mill, to about 1600 F. as it leaves the mill after the last pass. All of the reduction in such conventional installations is done by one set of rolls, and so it is understandable that the roll surfaces, operating under these temperatures and heavy Working pressure conditions (a pressure load of several million pounds is not uncommon), will deteriorate rapidly. Consequently, the surface quality of the product produced by the conventional reversing hot strip mill is not entirely satisfactory. The surface is generally rough and the strip is not useable where a fine surface finish is required. To maintain a satisfactory, acceptable surface quality under such operating conditions, requires that the rolls be changed about every fifth or sixth coil. Such frequent roll change is expensive, time consuming and reduces the overall output tonnage of the mill.

In contrast to the usual single stand reversing hot strip mill, the mill of the present invention selectively utilizes tandem roll stands and produces products having a surface quality equivalent of the surface quality produced by the fully continuous and semi-continuous type hot strip mills. In the present invention, the No. 1 roll stand is selectively used as an intermediate roughing roll, and the No. 2 roll stand is selectively used for only the last two pases as a finishing roll stand. The temperature of the strip during the last two finishing passes in a typical installation is between 1650" F. and 1600 F., and because the reduction in thickness is considerably less than during the intermediate roughing passes, the pressures are consequently lower. Hence, the second set of rolls will stay bright longer and will impart the good bright surface, characteristic of a high quality product, for a longer period of time than the usual single stand mill.

The versatility and effectiveness of the present invention is demonstrated in another manner. When, in the course of normal operation, it becomes necessary to remove the rolls in the No. 1 intermediate roughing stand because of wear, for example, they are replaced with new rolls, or resurfaced rolls. The rolls in the No. 2 finishing stand, which have been used less severely are relatively bright and useful. Thereafter, the No. 2 roll stand be- Comes the intermediate roughing roll stand (replacing the No. 1 roll stand) and the No. 1 roll stand, with the new rolls, becomes the No. 2 finishing roll stand.

It should be apparent, then, that the operative life of the mill of the present invention is long and the operative life of the rolls, in tonnage produced, is great.

From the foregoing it will be apparent that the reversing hot strip mill of the present invention has many features and advantages not known heretofore. The mill of the present invention is extremely versatile and flexible in operation. It is relatively inexpensive and it produces hot strip metal that equals in quality the product produced by the finest type continuous strip rnill.

I claim:

I. The method for producing strip metal comprising the steps:

(a) arranging first and second roll stands in an adjacent tandem relation;

(b) spacing apart the rolls of said first roll stand to allow free passage therethrough of a strip of metal;

(c) passing and repassing said strip of metal freely through said first roll stand and in engagement with the rolls of said second roll stand a plurality of times, and adjusting the spacing of the rolls of said second roll stand between passes so that said strip of metal is reduced in thickness during each successive pass through said second roll stand; thereafter (d) spacing apart the rolls of said second roll stand to allow free passage therethrough of said strip metal;

(e) adjusting the rolls of said first roll stand to engage said strip of metal; and

(f) freely passing said metal strip at least once through said second roll stand and into engagement with the rolls of said first roll stand whereby the thickness of said metal strip is reduced to a preselected thickness and is surface finished.

2. The invention of claim 1, including the step:

(a) passing said metal strip through said first and second roll stands after adjusting the rolls of said first roll stand to engage said strip of metal a plurality of times, and adjusting the rolls of said first roll stand between each pass to reduce the thickness of said metal strip on a successive pass; and

(b) passing said metal strip through said first rolls a last time to surface finish said metal strip.

3. The method of claim 2 including:

(a) reheating said strip of metal after each pass.

4. The method of rolling metal strip utilizes first and second roll stands arranged in tandem wherein the improvement comprises the steps:

(a) adjusting the rolls of said first roll stand to freely pass said metal strip without reducing the thickness thereof;

(b) passing and repassing said metal strip a plurality of times freely through said first roll stand and in engagement with the rolls of said second roll stand;

(0) adjusting the spacing of the rolls of said second roll stand after each pass therethrough so that the thickness of said metal strip is reduced during the next succeeding pass; thereafter ((1) adjusting the spacing of the rolls of said second roll stand to freely pass said metal strip without engaging said metal strip;

(e) adjusting the rolls of said first roll stand to engage said metal strip; and

(f) passing at least once said metal strip freely through the rolls of said second roll stand and engagingly through the rolls of said first roll stand to reduce the thickness of said metal strip to a preselected thickness.

5. The method of claim 4, including the step:

(a) passing said metal strip through the rolls of said first roll stand a last time to surface finish said metal strip and freely through the rolls of said second roll stand.

6. The method of claim 4 including the step:

(a) reheating said metal strip between successive passes through said roll stands.

7. The method for rolling metal strip utilizing first and second roll stands arranged in tandem wherein the improvement comprises the steps:

(a) passing and repassing said strip of metal through said first and second roll stands a plurality of times and after each pass adjusting the rolls 01? said second stand only to engage and reduce the thickness of said strip; thereafter (h) adjusting the rolls of said first roll stand to engage said metal strip;

(c) passing said strip through said first and second roll stands at least once to reduce the thickness of said strip as it passes through said first roll stand; and

(d) passing said strip through said first and second roll stands a last time whereby said first rolls reduce the thickness of said strip to a desired gauge thickness and surface finish the same.

References Cited WILLIAM W. DYER, 1a., Primary Exmnincr.

GERALD A. DOST, Examiner. 

1. THE METHOD FOR PRODUCING STRIP METAL COMPRISING THE STEPS: (A) ARRANGING FIRST AND SECOND ROLL STANDS IN AN ADJACENT TANDEM RELATION; (B) SPACING APART THE ROLLS OF SAID FIRST ROLL STAND TO ALLOW FREE PASSAGE THERETHROUGH OF A STRIP OF METAL; (C) PASSING AND REPASSING SAID STRIP OF METAL FREELY THROUGH SAID FIRST ROLL STAND AND IN ENGAGEMENT WITH THE ROLLS OF SAID SECOND ROLL STAND A PLURALITY OF TIMES, AND ADJUSTING THE SPACING OF THE ROLS OF SAID SECOND ROLL STAND BETWEEN PASSES SO THAT SAID STRIP OF METAL IS REDUCED IN THICKNESS DURING EACH SUCCESSIVE PASS THROUGH SAID SECOND ROLL STAND; THEREAFTER (D) SPACING APART THE ROLLS OF SAID SECOND ROLL STAND TO ALLOW FREE PASSAGE THERETHROUGH OF SAID STRIP METAL; (E) ADJUSTING THE ROLLS OF SAID FIRST ROLL STAND TO ENGAGE SAID STRIP OF METAL; AND (F) FREELY PASSING SAID METAL STRIP AT LEAST ONCE THROUGH SAID SECOND ROLL STAND AND INTO ENGAGEMENT WITH THE ROLLS OF SAID FIRST ROLL STAND WHEREBY THE THICKNESS OF SAID METAL STRIP IS REDUCED TO A PRESELECTED THICKNESS AND IS SURFACE FINISHED. 